Numerous methods and materials exist for the construction of retaining walls. Such methods include the use of natural stone, poured in place concrete, masonry, and landscape timbers or railroad ties. In recent years, segmental concrete retaining wall units which are dry stacked (i.e., built without the use of mortar) have become a widely accepted product for the construction of retaining walls. Such products have gained popularity because they are mass produced, and thus relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install, and couple the durability of concrete with the attractiveness of various architectural finishes.
It is desirable to build a wall from such blocks quickly and without the need for special skilled labor. The efficiency of building a wall can be measured by determining how fast the front face of a wall is constructed. Clearly, this depends on the size of the blocks used and ease of stacking the blocks.
It is standard practice in the prior art to use similarly sized mold boxes to produce various styles of block. For example, a standard size box has a block molding area of about 18 inches by about 24 inches (about 45.7 cm by about 61 cm), and produces a block about 8 inches (20.3 cm) thick. FIG. 1A illustrates retaining wall block B1 in mold box M. This block is symmetrical about a centrally located vertical plane of symmetry. Block B1 has pin holes PH, pin receiving cavities PC, and two cores C1 and C2. The sides generally converge from the front to the back of the block. Front face F is produced by the removal of waste portion W after the block has formed. This portion is split off to form a roughened surface. The block of FIG. 1A is manufactured one block at a time so that the yield per cycle is one square foot (1 sq ft or 929 sq cm) of front face. A typical weight for this block is about 110 lbs (50 kg).
Other prior art blocks are shown in FIGS. 1B and 1C in mold box M. This block is similar to that described in WO 02/101157 (MacDonald et al.). This block also has similarities to block B1, as it is symmetrical about a centrally located vertical plane of symmetry. Block B2 has pin holes PH, pin receiving cavities PC, and core C. Preferably, the blocks are formed so that front face F will have a roughened appearance. Block B2 is made in a mold box two at one time. This provides a good use of mold space, producing about two square feet (1858 sq cm) of front face per manufacturing cycle. FIG. 1B illustrates that the blocks can be formed two at a time and separated at the back faces. In this case, the front surface of the block is textured by texturing elements T that contact the front surface as the block is removed from the mold box. FIG. 1C shows blocks that are molded together at front face F. The front faces of these blocks will be separated, or split apart after curing. The splitting of such blocks is used to form the desirable surface appearance. When manufactured in this manner, each block has a front face of about one square foot (1 sq ft or 929 sq cm). Thus, the yield per cycle is two square feet of front face. A typical weight for this block is about 85 lbs (38.6 kg).
A third type of prior art block in its mold box M is shown in FIG. 1D. Block B3 is a rectangular block, shown having two cores or cavities C. The long dimension of the block typically is used to form the face of a wall. Thus, this type of block produces a useful front surface about 24 inches long, rather than the 18 inch long surface of blocks B1 and B2. The surface area (for the same thickness block, i.e., about 8 inches) is about 33% greater than the surface area of blocks B1 or B2. However, this block weighs about 250 lbs (113.6 kg) and must be set in place using mechanized means.
Accordingly, a need in the art remains for wall blocks that make the most use of a mold box's area while producing a block with a large front surface area.